1. Field
Disclosed herein is a composition for an adhesive material and a use of this composition in particular for gluing electronic components.
2. Description of Related Art
In the manufacturing of inductive components, adhesives are required for a wide variety of joining and assembly processes. In this case, materials based on a wide variety of chemicals are commonly used both in ready-to-use single-component formulations and in multi-component formulations, which are to be mixed only immediately before use. In turn, the latter can be categorized as room-temperature-hardening systems and as adhesive materials that harden at elevated temperatures.
For applications with increased requirements with regard to adhesive strength and temperature stability, here in general adhesives based on epoxide resins have gained acceptance in practice. Because of their significantly simpler handling, which from the start eliminates processing errors due to inadequate mixing conditions or insufficiently thorough mixing, single-component adhesives, especially in the case of thixotropic or paste-like adhesive materials, are significantly more common than the two- or multi-component products that predominate in the case of materials—especially casting resins with lower viscosity.
While it is generally readily possible—in the case of the adhesives that are to be mixed and that consist of several separate components—to adapt to the most varied requirements such as shelf life or limited hardening temperatures, here finish-formulated single-component systems are subject to significantly more extensive limitations. In electronics manufacturing, it is absolutely imperative to avoid premature aging of the components to be processed or their soldered connections. As a consequence, it is necessary to use adhesives with the lowest possible hardening temperature and the shortest possible hardening time. While this is unproblematic in the case of two-component systems that are to be mixed, in the case of single-component adhesives, the problems exist in principle that at low temperatures, fast-hardening adhesives have an adequate shelf life only at very low temperatures or that mixtures with a long shelf life at room temperature generally require hardening temperatures around or above 150° C., which in turn has a very disadvantageous effect on the properties of the electronic components to be processed, especially their subsequent solderability.
To solve this problem, a commonly used approach for single-component adhesives is the use of a combination of hardeners with hardening accelerators that are generally soluble in the resin components only at elevated temperatures, which accelerators are activated only at elevated temperatures in a chemically active form, e.g., by cleavage of a low-molecular compound that blocks the active group. As standard hardeners for these applications, engineering practice has adopted finely-ground (micronized) dicyandiamide, which without additional hardening accelerators makes possible mixtures that have a good shelf life but that require hardening temperatures of above 150° C.
For reduction of the hardening temperature, catalysts based on substituted urea derivatives, such as, for example, 3-(4-chlorophenyl)-1,1-dimethylurea (monuron) or 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) in amounts of below 1% by weight, relative to the amount of resin, are commonly used. With these additional accelerators, hardening temperatures in the range starting from about 120° C. are accessible.
Another technically-established variant is the use of blocked amine or imidazole complex compounds. Typical representatives of these two substance classes were, for example, zinc-bis[(tetramethylguanidine)-(2-ethylhexanoate)] or, for example, zinc-bis[(1-methylimidazole)-(2-ethylhexanoate)]. Even when using these complex compounds, which are added in amounts of typically 0.1 to 1% of the formulation, hardening temperatures starting from approximately 120° C. in connection with dicyandiamide are possible. It has been shown, however, that these adhesives, hardened with dicyandiamide and optionally additional hardening accelerators, specifically meet the requirements for a sufficiently low hardening temperature with good adhesion to typical structural materials and good long-term temperature stability, but typically only achieve creepage current resistance values in the range of 350 to 450 V in the examination of creepage current resistance according to DIN EN 60112, and thus are to be assigned to the insulating material class II or IiIa. This is disadvantageous to the extent that for the manufacturing of inductive components, there are a number of structural plastics that achieve creepage current resistance values of greater than 600 V and thus insulating material class I. If these plastics (e.g., polyamide 6,6, polyamide 6,6T or polybutylene terephthalate) are used as insulating materials and at the same time an adhesive connection of various components is performed, it is no longer the higher-grade material of the insulating material class I but rather the considerably poorer adhesive of the insulating material class II or IiIa that determines the necessary geometric minimum gaps (creepage distances) and thus the component sizes.